Method for fabricating articles of hard metal compositions



E. W. ENGLE METHOD FOR FABRICATING ARTICLES OF HARD METAL COMPOSITIONS July 5, 1938.

Filed Aug. 4, 1934 Edgar Wing/e 1 Km -0- MM.

ATTORNEYS Patented July 5, 1938 UNITED STATES METHOD FOR FABRICATING ARTICLES OF HARD METAL COMPOSITIONS Edgar W. Engle, Hastings on Hudson, N. Y., as-

signor,

by mesne assignments, ,to Carboloy Company, In'c., a corporation of New York Application August 4, 1934, Serial No. 738,472

4 Claims.

This invention relates to hard metal compositions and particularly to methods for reclaiming and resizing broken or worn dies and tools made of hard metal compositions and to the shaping of articles made of such compositions. The metal compositions with which this invention is concerned are sintered hard metal alloys in which hard material consisting of carbides of one or more of the refractory metals of the fourth, fifth and sixth groups of Mendelejeffs periodic table of elements, is embedded in a matrix of a softer and more ductile metal having a lower melting point. These hard metal alloys include the general class of alloys to which be long the hard metal alloys disclosed in the Schriiter Letters Patent of the United States, Nos. 1,549,615 and 1,721,416, and a practical form consists mainly of tungsten carbide and a metal of the iron group. Among other metals (and their carbides) that may be used with or instead of tungsten, mention may be made of tantalum, titanium, molybdenum and columbium. Such hard metal compositions may be identified as cemented hard metal carbides and the use of that term in the following claims is to be understood as conveying that meaning.

Articles such as dies and cutting tools which are made from these compositions are exceedingly hard and tough and except for grinding and polishing, these articles are usually made in the forms in which they are to be used. But after extended use of a die nib, for example, the working surface thereof becomes worn and the die hole is enlarged beyond the tolerance permissible in the manufacture of the Wire for the drawing of which the die nib was originally designed. Other causes resulting in disuse or waste are prevalent and it sometimes happens that a die nib will split or that pieces will be chipped from the orifice of the die hole so as to render the die nib unusable. The initial cost of the die nibs is sufficiently great to justify their repair, but

methods which have been heretofore used for repairing have not proven altogether'satisfactory because of the expense involved and the uncertainty of producing a repaired die which is good enough for the purposes for which the die was originally used. Consequently, it has been the general custom to discard such articles when they have become broken or when they have become too worn to be of further use.

The qualities which make these compositions satisfactory for wire drawing have not been im-' paired or diminished in the least because of use or of failure of the-die nib, and it is among the (Cl. 76-107) objects of the present invention to enable reclamation of brokenand worn dies so as to again make available and useful the original properties of the composition in a die nib as satisfactory as the original article.

Another. object of my invention is to provide a novel method for reforming and resizing dies and cutting tools made from hard metal compositions, and to reshape or reduce the size of the die hole of either a worn or a new die nib.

Other objects and advantages of the invention .will appear in more detail hereinafter in connection with the accompanying description of apparatus with which the method may be practiced.

In the drawing:-

Fig. 1 is a plan, partly in section, of the heating chamber of the furnace shown in Fig. 2. 1 Fig. 2 is a sectionalelevation of a combined press and furnace by which the invention may be practiced.

Fig. 3 is a modified form of heating and forceapplying apparatus.

Fig. 4 is a form of wire drawing die nib which has been split. I

The most common failure of adie nib is the longitudinal cracking in two or more places, with breaking into several parts. In reclaiming such dies I first make certain that all foreign matter has'been removed from the surfaces which are to be united. The pieces are then assembled together and subjected to heat and pressure in such.- a manner that union takes place. All of the useful properties of homogeneity, hardness and toughness are maintained in the reclaimed or reshaped article. If foreign material is present the die nib is cleaned. Grease and dirt may be removed by an organic solvent or by alkali cleaners. While adhering foreign material may be removed by any mechanical or chemical means which is suitable for this purpose, adhering steel may be removed with hydrochloric acid and ad'- hering copper may be removed with nitric acid. A final cleaning with hydrofluoric acid to which a small amount of nitric acid has been added will remove adhering metallic oxide and leave the surfaces clean with a dull metallic surface. Sufficient care should be. taken in the cleaning operations that as little as possible of the die nib material is removed, but even if the contiguous surfaces do not fit closely together, a good joint will be obtained. I

The various pieces or broken parts of the die nib are assembled and the whole is reduced to a plastic state by the application of heat. I prefer utilizing an extrusion process for developing' the pressure desired, and the pressure should be sufiicient to maintain a steady rate of slow flow. The temperature used depends upon the materials and the proportions of the materials which are present in the composition of the article being processed. For a composition consisting of tungsten carbide and cobalt in the proportions of about 6 to 7% carbon, 7 to 8% cobalt, and the remainder of the whole content,

tungsten, I have found that the desired results may be obtained under temperatures ranging from 1600 C. to 1700" 0., whereas for the other hard metal alloys with which this invention is concerned and having a cobalt, nickel or iron content range of from 3% to 20%, the temperature ranges from 1500 C. to 1800 C. Pressure is appplied until complete union of the parts takes place and with the temperature properly regulated within the limits stated. I have found that a pressure of a few hundred pounds per square inch is sufficient to make the material flow together into an homogeneous mass.

The heating and pressing operations are accomplished in a neutral or reducing atmosphere. Such an atmosphere may consist of hydrogen, cracked ammonia, hydrocarbons, or other noninjurious gases. The inert or reducing atmosphere protects against decarbonization and oxidation and keeps the surfaces clean;

While various methods of heating known to the art may be used, I prefer to heat by electrical means whereby the material or the forming die or both are heated by direct electrical resistance, or by means of high frequency induced currents. Such methods enable close regulation and provide for a high degree of localized control of the temperature. Auxiliary heating or indirect heating may be accomplished by the use of silicon carbide resistance rods or molybdenum wire. Where the forming dies or punches are to be used also as heaters, the use of graphite or carbon for such parts is preferred.

In the drawing, I have shown a combined furnace and press which I have found suitable for practicing the method of the present invention. Upon the lower table ill of the press there is mounted a furnace casing or insulating packing H of some such material as Alundum or fire brick. In the base of this furnace casing there is an electrode I2 in the form of a box made of conducting material, such as graphite. Over an opening in the box there is mounted an extrusion die IS in which the die nib or other article to be reclaimed or constricted, is extruded. A pair of silicon carbide resistance rods l4, 14, act as indirect or auxiliary heating elements and these contribute to maintain the furnace at a uniform and desired temperature.

The head I 5 of the press carries a punch holder IE to which the punch l1 and the refractory insulating sleeve I8 are attached. The punch holder, punch and extrusion die are made of graphite and the main heating current is conducted through the punch and extrusion die and through the die nib therebetween. l0 and head IS, the press and the electrode supporting members [9 are water cooled in a manner customary in this type of apparatus.

After making sure that the pieces of a' broken die are clean they are assembled together and then placed in assembled form within the upper portion of the extrusion die. Preferably a graphite washer (not shown) is placed between The table .back of the material of the die nib and to keep the material away from the punch. The die nib is maintained in an atmosphere of an inert or reducing gas which is introduced to the furnace through an opening 20 in the electrode box l2.

The furnace, extrusion die and the die nib are then. preliminarily heated by the resistance rods I4, i4. With the engagement of punch H with the die nib the heating of the latter is augmented and brought up to temperature by the passage of current therethrough and between the punch and the extrusion die. When the temperature has reached that at which the material becomes plastic the press is operated to cause the extrusion of the die nib through the extrusion die.

While the rate of movement of the approaching elements of the press may vary somewhat, it is relatively slow, and for a die nib having a height and a diameter of about of an inch each, for a reduction in diameter of approximately 50 thousandths of an inch, the time for the passage of the die through the extrusion die should be in the neighborhood of 2 or 3 minutes. This specification for the time of passage is not invariable and is given only for afford,- ing general instruction, it being subject to different factors including the size and kind of article, the degree of constriction to be attained, the composition of the article, and its degree of plasticity. The hole in the extrusion die is cut back at its lower end so as to permit the ejection of the die nib.

So as to enable removal of successive die nibs from below the extrusion die a. plunger 2| of refractory material is provided whereby the die nibs may be displaced within the box I2. The

removal of the plunger from the box leaves a passage for the removal of the extruded die nibs.

It will be understood that the choice of punch and extrusion die is dependent upon the sizes and kinds of articles which are to be processed. If it is desired only to resize the die hole of a die nib, the minimum diameter of the die hole in the extrusion die may be so chosen as to cause the constriction of the die hole in the die nib to the size desired. The die hole may be later ground to the desired dimensions in the event that the extrusion process has reduced it excessively. The outside dimensions of metal composition stock to be used for cutting tools may be reduced or reshaped by the method of my invention.

A modified arrangement for applying heat and pressure is illustrated in Fig. 3 in which the press is provided with a pair of heating punches 22, 23,.

in which there is mounted a mandrel 24, which may be cylindrical or tapered, and of any desired cross-sectional shape. This mandrel is of such size and shape as to produce the desired form of die hole. The broken pieces of a broken die nib are assembled within the hole of a. die member 25 and between two washers 26 and 21, at least one of which has a snug engaging fit with the mandrel whereby the latter is maintained in proper relationship to the material being processed. The temperature is'obtained by the passage of current between the heating punches 22 and 23 and pressure is exerted upon the die nib -by the movement of the two punches towards each other and against the broken parts therebetween. This construction is suitable for moldor without the use of a mandrel.

The method is carried out with the aidof this apparatus in much the same manner in which it is carried out by the use of the apparatus shown in Figs. 1 and 2, but the fabricated or reclaimed die nib is forced out of the die member 25 mechanically. The size of the die hole maybe in-' creased or the die nib may be given any desired configuration by grinding in accordance with the methods generally used for shaping and finishing.

A die nib which has been fractured into two parts in the manner illustrated in Fig. 4 may be repaired by first cleaning and uniting the two parts and then heating the same to the temperature productive of a plastic condition of the material. This may be accomplished between two graphite electrodes which bear upon diametrically opposite sides of the die nib and are adjustable to exert pressure to press the contiguous surfaces together. When the desired temperature has been reached, and union of the contiguous surfaces has taken place, the die nib is then removed from the furnace and in the event the pressure exerted by the electrodes has caused distortion, it may be extruded while heated so as to restore its original shape. This latter operation may be performed in a furnace of the type illustrated in Figs. 1 and 2, if desired. Thereafter the die hole may be ground to the size desired if the preceding operations have effected a change in the original dimensions of the die hole.

It is to be understood that the invention is not limited to the specific construction herein illus-' trated and described. but can be embodied in other forms without departure from its spirit.

What is claimed is: 1. The method of reclaiming a worn or broken 'die nib made from cemented hard metal carbide,

properties of the original die nib throughout and the die hole to be reconditioned.

2. The method of rebuilding a broken die nib made from cemented hard metal carbide, which comprises assembling together the broken pieces of the die nib to be rebuilt in the same relative positions they originally were in, heating the assembled pieces in a protecting atmosphere, and forcing the assembled nib through a graphite extrusion die having a restricted passage to apply pressure to the-heated pieces until the combined heat and pressure cause union of the separate pieces into a single mass comprising a nib having substantially the same characteristic properties of the original die nib throughout.

3. The method of rebuilding a broken die nib made from cemented hard metal carbide. which comprises cleaning the surfaces of the broken pieces of the die nib to be rebuilt, assembling together the cleaned pieces of the nib in the same relative positions they originally were in, heating the assembled pieces in a protecting atmosphere to a temperature of the order of about 1500 0., and forcing the assembled nib through a graphite extrusion die having a restricted passage to apply pressure to the heated pieces until the combined heat and pressure cause the contiguous surfaces of the pieces to weld together autogenously into a single masscomprising a nib having substantially the same characteristic properties of the original die nib throughout.

4. The method of reclaiming a worn or broken die nib made from cemented hard metal carbide, which comprises heating in a protecting atmosphere a complete die nib having the various portions thereof arranged in substantially the same 

